Microsystems and nanotechnology - MiNaLab

Nanotechnology and materials science requires very sophisticated equipment. In MiNaLab we have state-of-the-art cleanroom facilities for advanced material research. The laboratory includes facilities and a complete silicon processing line for the University of Oslo (SMN) and SINTEF.

These facilities are available for researchers, students and external companies. A brief introduction to our infrastructure will be presented here.

The cleanroom at MiNaLab.

Photo: Geir Mogen

Equipment at MiNaLab

Advanced tools for synthesis, processing and characterization are available at MiNaLab.

1. Optical characterization

Brief description of XRD

MiNaLab has a high resolution X-ray diffraction (XRD) instrument for studying thin films. This instrument uses a copper x-ray source to study diffraction in polycrystalline and epitaxial thin films. Given a certain x-ray wavelength and incident angle, the distance between crystal planes can be determined. By rotating the sample and the x-ray detector, different crystal planes can be studied to produce a fingerprint of the sample. This fingerprint can be looked up in a database to determine which crystals are present in the sample and to what degree they are found.

Brief description of UV-VIS-NIR

This instrument is built for studying the transmission and reflection of light in a given material. The name is short for ultra violet (UV), visible (VIS) and near infra red (NIR) to indicate the wavelengths covered by the instrument. Studies of transmission and reflection are important in materials intended for light emitting diodes (LED) or solar cells. Transmission spectra can also be used for studying band gaps of semiconductors, since only light with energy below the bandgap is transmitted.

Brief description of Photo Luminescence (PL)

This technique involves excitation of the electrons of a sample surface by application of a laser light. Often these excited electrons will relax and fall into the conduction band before emitting a photon and settling in the valence band. This roundtrip may involve many steps and the emission of several photons, giving valuable information about the electron structure of the material.

2. Electrical characterization

Brief description of electrical characterization at MiNaLab

For electrical characterization we have equipments for measuring various electrical parameters such as; voltage, current, capacitance and conductance. This gives the possibility of performing current-voltage (IV), capacitance-voltage (CV) and conductance-voltage (GV) measurements. In combination with the possibility of varying the temperature and frequency, characterization methods such as; deep level transient spectroscopy (DLTS), temperature stimulated current (TSC), impedance spectroscopy (IS) and admittance spectroscopy can be performed.

In the electrical characterization lab, we have five setups all with slightly different properties related to the sample holders, frequency range and cooling systems. Three of the setups use liquid nitrogen (LN2, which can reach 77 K) as the cooling source and operate at atmospheric pressure. The two last setups have sample chambers that can be pumped to low vacuum, and use a helium gas cryo pump for cooling. If proper vacuum conditions exist, these setups can measure down to 10 K. All but one of these five setups have an upper temperature limit of about 350 K, while one of the setups based on LN2 can be operated up to 700 K. As all of the sample holders have an internal heating element, the temperature can be stabilized at a desired temperature during measurements. Of the mentioned setups, the sample holders for low temperature measurements have a sample size limitation of ~1x1 cm2. Whereas samples of ~2x2 cm2 can be handled in the sample holder which uses LN2 as the cooling source.

In the cleanroom, there are dedicated setups for performing various electrical characterizations. We have a quasi steady-state photo conductance (QSSPC) for lifetime measurement and a four-point probe for resistance measurement of bulk and thin films, both operating at room temperature. In addition, we have a Hall-setup with a vacuum and cooling system similar to the aforementioned low temperature systems which have a temperature range of 10-350 K. There is also a setup capable of performing IS at high temperature in different atmosphere.

3. Chemical and physical characterization

Methods for chemical analysis: SIMS, XPS.

Brief description of SIMS

Secondary ion mass spectrometry (SIMS) is a technique used in materials science and surface science to analyze dopant elements and impurities in solids and thin films by sputtering the surface of the specimen with a focused primary ion beam and collecting and analyzing ejected secondary ions. These secondary ions are measured with a mass spectrometer to determine the elemental, isotopic, or molecular content/concentration. SIMS is one of the most sensitive surface analysis technique, being able to detect elements present in the parts per billion range.